This invention relates to a vertical roller mill of the type used for comminuting solid materials such as coal, cement raw meal, cement clinker and ores. More particularly, the invention relates to an improved apparatus for exerting a downward force on the grinding roller of such a roller mill.
The invention is directed to a vertical roller mill which includes a casing or mill body with a horizontal grinding table mounted for rotation about a vertical axis positioned within that casing. Suitable drive means such as a motor and gear reducer are provided for rotating the table. One or more rollers are also mounted in the casing for rotation about an axis which is at some angle to the table. A downward force is exerted on the roller so that a bed of material on the table will have compressive and shear forces applied to the material to thereby comminute the material. Various means may be provided for removing the material from the table such as air which flows through the mill to lift the fine ground material up to the top of the casing where an air classifying device allows the fine particles to exit through the top of the mill and coarse particles to be recirculated back to the table. Other mills of this type include an overflow discharge for material so that material is discharged from the bottom of the mill and mechanically conveyed to a separator. Mills of the type to which the present invention relates are shown for example in U.S. Pat. Nos. 4,218,023 issued Aug. 19, 1980; 4,339,086 issued July 13, 1982; 4,694,997 issued Sept. 27, 1987; 4,382,558 issued May 10, 1983; 4,483,487 issued Nov. 20, 1984; 2,342,255 issued Feb. 22, 1944 and others.
One type of apparatus for exerting a force on the roller is shown in my prior U.S. Pat. No. 4,694,997.
Prior to the present invention, one type of a vertical roller mill known as a Loesche mill included grinding rollers mounted on one end of a pivotally mounted rocker arm assembly. This assembly is pivoted approximately its mid-point. A hydraulic piston-cylinder apparatus within the roller mill housing pulls on the other end of the rocker arm so that the rocker arm pivots about its connection to the mill body and a downward force is exerted on the grinding roll. This arrangement is shown in the aforesaid U.S. Patents including my own prior patent.
Prior designs result in congestion inside the mill stand and mill body making details and assembly difficult. The mechanical advantage of the prior design is limited thus requiring a large diameter hydraulic piston cylinder or force exerting means.